In the manufacture and operation of engines such as diesel engines and Otto cycle internal combustion engines, it is well known to employ a cam shaft to coordinate the timing of valve opening and closing and to inject fuel. For example, with a diesel engine, an engine block is provided having a plurality of cylinders therein. A plurality of pistons are reciprocatingly mounted within each of the cylinders with a plurality of valves associated with each the cylinders to allow for inflow and outflow of air. In order to coordinate the timing of those valve openings, each valve is typically in forced contact with one end of a rocker arm or cam follower. This is typically accomplished with a push rod or other components comprising the valve train. The rocker arm itself is pivotally mounted relative to the engine block. One end of the rocker arm is provided with a rotating element called a roller which engages cams mounted on the cam shaft. Each cam is eccentrically formed so that rotation of the cam shaft causes larger and smaller diameter portions of each cam to rotate and in turn cause the rocker arm to pivot, thus opening and closing the valves and/or engaging a fuel injector plunger, as appropriate.
While effective, for such structure to operate effectively and consistently, the roller needs to be able to freely rotate at all times. Any inhibition or prevention of such rotation detrimentally affects the operation of the engine. If the roller were to seize on the rocker arm, for example, operation of the engine may be even more affected thus resulting in catastrophic failure.
With some rocker arms, the roller is mounted to the rocker arm using a complicated assembly of components. More specifically, an internal pin or axle extends between first and second sides of the rocker arm with an inner race being rotatively mounted to the pin. A bushing is then provided around the inner race with the roller itself then being mounted onto the bushing. Given the relatively small dimensions of such components, the assembly and manufacture of such a device is fairly complicated. Moreover, given the tight tolerances between the components, the bushing and inner race must be press fit together also adding to the difficulty and manufacturing cost associated with such a rocker arm assembly. In addition, such an assembly typically employs a lead tin overlay which adds to the complexity and cost of the assembly as well.
From the foregoing, it can be seen that a need exists for an improved rocker arm and roller assembly.